Navigation device for an optical system for aiming and observing a scene, and method for determining the attitude of such an optical system

Abstract

A navigation device (3), configured to be rigidly mounted on an optical scene observation and targeting system (SC), the navigation device (3) comprising an inertial module (31), a vision module (32), at least one database (33) storing a plurality of reference attitudes (Ari), each associated with a reference optical signature (Sri), a computer (34) configured to compare a current inertial attitude (Ac) to the reference attitudes (Ari) so as to determine the nearest reference attitude (Arp) and deduce the associated reference optical signature (Srp), compare the current image (IMc) captured by the vision module (32) with the associated reference optical signature (Srp) so as to determine an angular offset (Δ), and determine the navigation attitude (An) from the nearest reference attitude (Arp) and the angular offset (Δ). Abstract figure: Figure 2

Description

Title of the invention: Navigation device for an optical system for aiming and observing a scene and method for determining an attitude for such an optical system Technical field

[0001] The present invention relates to a navigation device for determining an attitude for an optical sighting and observation system, for example, optronic binoculars or a terrestrial sight. The invention aims in particular to propose a navigation device providing an attitude having reduced drift.

[0002] An optical sighting and observation system, hereinafter "optical system", makes it possible to observe a scene remotely to determine, for example, movements of people or activities. Such an optical system is portable or fixed. In order to precisely determine the position of the observed scene, the optical system is associated with a navigation device making it possible to determine the angular orientation of the optical system. The angular orientation is known to those skilled in the art under the designation "attitude". Precise knowledge of the attitude for the optical system makes it possible to carry out modeling, observe several zones associated with different angular positions quickly. This advantageously makes it possible to automate shots or shots or to geolocate friendly or enemy targets.

[0003] In a known manner, a navigation device comprises at least three gyroscopes for determining the attitude. During its initialization, the navigation device is calibrated with an astral sighting device or the like in order to determine an initial attitude accurately. In practice, the gyroscopes generate an attitude drift which increases over time, potentially distorting the determined attitude. At long distances, an imprecise attitude can distort the aiming and, for example, cause a shot to fail. An immediate solution would be to carry out frequent calibration operations with the astral sighting device in order to reduce the drift. This requires interrupting the observation mission frequently, which presents a major drawback. It is therefore not possible to carry out observations lasting several hours.

[0004] In the prior art, it has been proposed to equip a navigation device with several accelerometers sensitive to the gravity field in order to correct attitude drift. However, such a solution is only applicable for an optical system moving along two axes and is not suitable for an optical system capable of moving along three axes such as a pair of optronic binoculars.

[0005] The invention thus aims to propose a navigation device, for an optical system which makes it possible to determine an attitude precisely and without imposing constraints on the operators. In addition, it is important that the navigation device maintains a low mass, a reduced size and is low energy consumption in order to be able to be used during military operations. PRESENTATION OF THE INVENTION

[0006] The invention relates to a navigation device, configured to be mounted securely on an optical system for aiming and observing a scene, the navigation device being configured to determine a navigation attitude, the navigation device comprising: • at least one inertial module, configured to determine a current inertial attitude continuously, • at least one vision module, configured to capture at least one current image of the scene continuously, • at least one database storing a plurality of reference attitudes, each reference attitude being associated with a reference optical signature, • at least one calculator configured for: • Compare the current inertial attitude to the reference attitudes in order to determine the closest reference attitude and deduce the associated reference optical signature, • Compare the current image captured by the vision module with the associated reference optical signature in order to determine an angular offset, • Determine the navigation attitude from the nearest reference attitude and the angular offset.

[0007] Thanks to the invention, any possible drift of the current inertial attitude can be avoided. A recalibration can be carried out dynamically when the current inertial attitude is close to a reference attitude of the database. The determination of an angular deviation from the current image makes it possible to visually measure any potential drift of the inertial module. In other words, the measurement of the relative movements between the images makes it possible to dynamically compensate for the drift.

[0008] According to one aspect, the calculator is configured to determine the associated reference optical signature only when the difference between the current inertial attitude and the closest reference attitude is less than a predetermined attitude threshold. Thus, when the reference data are too far from the point of the current attitude, any recalibration is avoided. A recalibration is only carried out in the presence of quality reference data nearby.

[0009] According to one aspect, the computer is configured to determine a new reference attitude associated with a new reference optical signature when the difference between the current inertial attitude and the closest reference attitude is greater than a predetermined attitude threshold. The database is advantageously completed when the operator observes attitudes that have not yet been listed. This makes it possible to carry out dynamic recalibrations subsequently when these attitudes are reached again.

[0010] According to one aspect, the new reference attitude corresponds to the current inertial attitude and the new reference optical signature is determined from the current image.

[0011] According to one aspect, the computer is configured to estimate, on the one hand, a first uncertainty for the current inertial attitude and, on the other hand, a second uncertainty for the navigation attitude, the computer being configured to use the current inertial attitude as the navigation attitude if the first uncertainty is less than the second uncertainty. The drift is thus controlled via the estimation of the uncertainty while avoiding an untimely correction.

[0012] According to one aspect, the inertial module and the vision module are physically integral in their movements.

[0013] According to one aspect, the inertial module comprises at least three gyroscopes in order to determine a precise inertial attitude.

[0014] The invention also relates to an assembly of an observation system and a navigation device as presented previously. Preferably, the navigation device is integrated into the observation system.

[0015] According to one aspect, the observation system is in the form of optronic binoculars or a terrestrial sight.

[0016] The invention also relates to a method for determining a navigation attitude by a navigation device as presented previously, the navigation device being mounted securely on an optical system for aiming and observing a scene, the method comprising steps consisting of: • Compare the current inertial attitude to the reference attitudes in order to determine the closest reference attitude and deduce the associated reference optical signature, • Compare the current image captured by the vision module with the associated reference optical signature in order to determine an angular offset, and • Determine the navigation attitude from the nearest reference attitude and the angular offset.

[0017] According to one aspect, the method comprises a step of initializing the current attitude by an astral sighting device. This makes it possible to obtain an ideal reference before carrying out an observation. It is thus possible to obtain quality reference data for the database at the start of the observation.

[0018] The invention also relates to a computer program type product, comprising at least one sequence of instructions stored and readable by a processor and which, once read by this processor, causes the steps of the method as presented previously to be carried out.

[0019] The invention further relates to a computer-readable medium comprising the computer program product as presented above. PRESENTATION OF FIGURES

[0020] The invention will be better understood on reading the description which follows, given by way of example, and referring to the following figures, given by way of non-limiting examples, in which identical references are given to similar objects.

[0021] [Fig.l] is a schematic representation of an operator observing a scene by means of an optical system on which a navigation device is mounted.

[0022] [Fig. 2] is a schematic representation of a navigation device according to one embodiment of the invention.

[0023] [Fig.3] is a schematic representation of a sighting point on a current image.

[0024] [Fig.4] is a schematic representation of a first example of aiming at a scene.

[0025] [Fig.5] is a schematic representation of a second example of aiming at a scene.

[0026] [Fig.6] is a schematic representation of the evolution of an attitude drift according to the prior art and according to the invention for an example of modification of the angular position.

[0027] It should be noted that the figures set out the invention in detail to implement the invention, said figures can of course be used to better define the invention where appropriate. DETAILED DESCRIPTION OF THE INVENTION

[0028] With reference to [Fig.l], there is shown an operator 2 observing an external scene SC at a long distance, by means of an optical system 1 for aiming and observation 1, hereinafter referred to as “optical system 1”. In this example, the system Optics 1 is a pair of optronic binoculars but it stands to reason that Optics 1 could be in the form of a sighting system mounted on a rifle or missile.

[0029] Preferably, the optical system 1 comprises an acquisition sensor, for example, a camera. Such an optical system 1 is known per se to those skilled in the art and will not be presented in more detail. In order to determine the orientation of the optical system 1, that is to say its attitude, a navigation device 3 is associated with the optical system 1.

[0030] In this example, with reference to [Fig.l], the navigation device 3 is fixed to the optical system 1 in a permanent or removable manner. The navigation device 3 is thus integral in its movements with the optical system 1. Any modification of the angular orientation of the optical system 1 induces a modification of the angular orientation of the navigation device 3.

[0031] It goes without saying that the navigation device 3 and the optical system 1 could be integrated into the same equipment. For example, the navigation device 3 could be directly integrated into a housing of the optical system 1.

[0032] [Fig. 2] shows schematically a navigation device 3 according to one embodiment of the invention. The navigation device 3 is configured to determine a navigation attitude An corresponding to that of the optical system 1.

[0033] With reference to [Fig.2], the navigation device 3 comprises: • an inertial module 31, configured to determine a current inertial attitude Ac continuously, • a vision module 32, configured to capture at least one current image IMc of the scene SC continuously, • a database 33 storing a plurality of reference attitudes Ari, each reference attitude Ari being associated with a reference optical signature Sri, • a computer 34 configured to determine the navigation attitude An from the current inertial attitude Ac, the current image IMc and the database 33.

[0034] The various elements of the navigation device 3 will now be presented. They are preferably powered by an electric battery not shown.

[0035] In this example, the inertial module 31 comprises three gyroscopes determining a current inertial attitude Ac of the navigation device 3, and therefore of the optical system 1. The current inertial attitude Ac is determined by reference to an initial attitude A0 obtained by calibration from an external navigation system, in particular, an astral sighting device or a compass. The current inertial attitude Ac is for example determined by integrating the angular velocities of the three gyroscopes. As presented in the preamble, the current inertial attitude Ac has an increasing drift over time. The current inertial attitude Ac is determined continuously by the inertial module 31.

[0036] In this example, the vision module 32 comprises an optical sensor, in particular a camera, directed towards the external scene SC. The vision module 32 is configured to capture a current image IMc of the scene SC continuously. It is specified that the current image IMc is independent of the images of the scene SC which are acquired by the optical system 1. It is nevertheless possible for the current image IMc to be identical to that acquired by the optical system 1. Preferably, the vision module 32 and the inertial module 31 are integral with each other in order to maintain consistency between the data. It goes without saying that the vision module 32 could belong to the optical system 1.

[0037] In this example, still with reference to [Fig. 2], the database 33 stores a plurality of reference attitudes Ari associated with a reference optical signature Sri and a reference date Dri. A reference optical signature Sri is determined from at least a portion of a current image IMc captured for said reference attitude Ari by the vision module 32. Preferably, the reference optical signature Sri is determined by an image processing algorithm. By way of example, the reference optical signature Sri corresponds to a set of data (generally a few thousand values) making it possible to estimate a geometric deformation between two images, in particular between the current image IMc and the image used to form the reference optical signature Sri.A reference optical signature Sri has a reduced weight and makes it possible to characterize the image visible by the vision module 32 when it is oriented at the reference attitude Ari. This makes it possible to have a database 33 having a large number of reference attitudes Ari while having a reduced weight. Thus, the database 33 can advantageously be entirely embedded. The mass and size of the optical sighting and observation system can thus be reduced. In addition, a reference optical signature Sri of reduced weight makes it possible to reduce the computing requirements and therefore the power consumption. This is particularly advantageous when the optical system 1 is embedded.

[0038] The reference date Dri corresponds to the current date at the time of determining the reference optical signature Sri. This advantageously makes it possible to delete the reference data Sri, Dri, Ari which have become obsolete due to their age. The reference date Dri is optional.

[0039] By way of example, with reference to [Fig. 3], the current image IMc seen by the optical device 32 is schematically represented when aiming at a point of reference Pi corresponding to the reference attitude Ari. In this example, a rectangular reference zone Zi is determined in the vicinity of the reference point Pi and the reference optical signature Sri is determined by calculation from the pixels included in the reference zone Zi. It goes without saying that the reference zone Zi could have a different shape.

[0040] With reference to [Fig.4], three reference points PI, P2, P3 are shown schematically, which correspond respectively to three reference attitudes Arl, Ar2, Ar3 associated with three reference optical signatures Sri, Sr2, Sr3 and three reference dates Drl, Dr2, Dr3.

[0041] The calculator 34 is in the form of a processor, a motherboard, an FPGA or the like and makes it possible to carry out calculation operations.

[0042] According to one aspect of the invention, as illustrated in [Fig. 2], the computer 34 is configured, according to a first step E1, to compare the current inertial attitude Ac with the reference attitudes Ari of the database 3 so as to determine the closest reference attitude Arp and to deduce therefrom the associated reference optical signature, hereinafter referred to as “closest optical signature Srp”. The reference date Drp of the closest optical signature Srp is also obtained in this example.

[0043] With reference to [Fig.2], the computer 34 is further configured, according to a second step E2, to compare the current image IMc captured by the vision module 32 with the closest optical signature Srp so as to determine an angular offset A.

[0044] According to one aspect of the invention, the optical signature corresponds to the average of the pixels on the lines and on the columns of the image. For example, to determine the angular offset A, the translations on the lines and on the columns are first determined by correlations between the signature of the current image IMc with the reference optical signatures Sri, Sr2, Sr3 so as to deduce a determined translation therefrom. Then, a geometric transformation is applied to transform the determined transformation into an angular offset A.

[0045] According to another aspect, the optical signature corresponds to high gradient pixels on the image. To determine the angular shift A, the geometric deformation is calculated which makes it possible to realign the high gradient pixels. It goes without saying that other methods could be suitable.

[0046] In practice, the current image IMc is realigned to the closest optical signature Srp in order to estimate the translation and rotation, i.e. a rigid deformation, between the current image IMc and the closest optical signature Srp. The angular offset A thus corresponds to a measurement of geometric deformation.

[0047] The computer 34 is further configured, according to a third step E3, to determine the navigation attitude An from the closest reference attitude Arp and the angular offset A. This advantageously makes it possible to correct any possible drift of the current inertial attitude Ac. Thus, the computer 34 makes it possible to determine a navigation attitude An which is based on measurements carried out in the past and which are deemed to be correct. Advantageously, this determination can be carried out routinely during the use of the optical system 1 by the operator 2. Preferably, the navigation attitude An, the closest reference attitude Arp and the angular offset A are linked by a mathematical formula which has been previously determined.

[0048] According to one aspect, the computer 34 is configured to estimate the quality of the navigation attitude An which has been determined, for example, according to the following criteria: angular speed lower than a fixed threshold, contrast level in the current image sufficiently high, etc. The computer 34 is configured to reject the navigation attitude An if the quality is too low.

[0049] Preferably, a navigation attitude An is determined only if the difference between the current inertial attitude Ac and the closest reference attitude Arp is less than or equal to a predetermined attitude threshold Sa. Indeed, if the difference is too great, the navigation attitude An which would be determined would lack precision.

[0050] Also, preferably, if the difference between the current inertial attitude Ac and the closest reference attitude Arp is greater than the predetermined attitude threshold Sa, the computer 34 is configured to store in the database 33 a new reference attitude Ari equal to the current inertial attitude Ac with a new reference optical signature Sri determined from the current image IMc. A reference date Dri is also associated with the new reference attitude Ari. This thus makes it possible to increase the size of the database 33 with reference attitudes that had not been determined in the past. When using the optical system 1, this will make it possible to accurately determine a navigation attitude An since the reference attitudes Ari will be more numerous.Similarly to previously, the computer 34 is configured to reject the new reference attitude Ari if the quality is too low.

[0051] According to one aspect, the computer 34 is configured to estimate, on the one hand, a first uncertainty for the current inertial attitude Ac and, on the other hand, a second uncertainty for the navigation attitude An. Preferably, the estimation of the uncertainties is carried out by computer learning or by integration of a previously calibrated error model. Preferably, the database 33 associates each reference attitude Ari with an uncertainty, that is to say, that of the current inertial attitude Ac when recording in the database 33.

[0052] If the first uncertainty is less than the second uncertainty, the computer 34 is configured to use the current inertial attitude Ac as the navigation attitude An. In other words, the navigation attitude An which has been determined is not retained due to its high uncertainty.

[0053] In order to maintain a database 33 having high relevance, the reference attitudes Ari associated with old reference dates Dri, for example dating back more than 20 minutes, are deleted in order to allow the storage of more recent reference data.

[0054] An example of implementation of the invention will now be presented with reference to Figures 4 to 5. In this example, with reference to [Fig.4], a scene SC is schematically represented in which three reference points PI, P2, P3 are represented which correspond respectively to three reference attitudes Arl, Ar2, Ar3 associated with three reference optical signatures Sri, Sr2, Sr3 and to three reference dates Drl, Dr2, Dr3. For the sake of pedagogy, the predetermined attitude threshold Sa is represented in the form of a circle for each reference point PI, P2, P3.

[0055] In practice, at the start of a mission, the database 33 does not include reference attitudes and these are learned during the mission. In this example, three reference attitudes Ar1, Ar2, Ar3 have already been learned.

[0056] Operator 2 wishes to observe the scene with optical system 1 and with vision module 32 of navigation device 3. He first calibrates inertial module 31 of navigation device 3 by means of astral sighting device. Thus, current inertial attitude Ac corresponds to initial attitude A0.

[0057] Then, as illustrated in [Fig. 4], the operator orients the optical system 1 with the navigation device 3 towards the scene SC according to a sighting attitude which is represented by a sighting point Pv in [Fig. 4]. In this example, the sighting point Pv is at the center of the current image IMc

[0058] The navigation device 3 determines the closest reference attitude Arp. For this purpose, the different reference optical signatures Sri, Sr2, Sr3 are compared to a zone defined in the vicinity of the aiming point Pv in the current image IMc. This comparison is carried out in this example by an image processing algorithm implementing correlation operations.

[0059] In this example, the third reference optical signature Sr3 is the closest. Also, the closest reference attitude Arp is the third reference attitude Ar3 associated with the third reference point P3. Since the difference between the current inertial attitude Ac and the third reference attitude Ar3 is less at the predetermined attitude threshold Sa as illustrated in [Fig.4], the navigation device 3 can determine a navigation attitude An from this third reference attitude Ar3.

[0060] The computer 34 firstly determines an angular offset A between the current image IMc captured by the vision module 32 and the third reference optical signature Sr3. It can then determine the navigation attitude An from the closest reference attitude Arp and the angular offset A. This practically gives a navigation attitude An which corrects any possible drift of the current inertial attitude Ac.

[0061] Preferably, as explained previously, if the current inertial attitude Ac has a low uncertainty, which is for example the case shortly after an astral calibration, the current inertial attitude Ac is used as navigation attitude An.

[0062] During the observation, the operator modifies the orientation of the optical system 1 as illustrated in [Fig.5]. The aiming point Pv is then modified. In this example, the third reference optical signature Sr3 is the closest. Also, the closest reference attitude Arp is still the third reference attitude Ar3 associated with the third reference point P3.In this example, given that the difference between the current inertial attitude Ac and the third reference attitude Ar3 is greater than the predetermined attitude threshold Sa, the navigation device 3 does not determine a navigation attitude An but stores in the database 33 new reference data by determining a fourth reference attitude Ar4 (corresponding to the current inertial attitude Ac) associated with a fourth reference optical signature Sr4 (determined in the current image IMc in the vicinity of the aiming point Pv) and with a fourth reference date Dr4.

[0063] Advantageously, the database 33 increases in size and makes it possible to increase the precision and to carry out dynamic calibrations during the use of the optical system 1.

[0064] With reference to [Fig.6], a first curve Ca shows the evolution of an angular position Pang of the optical system 1 over time. As illustrated in this figure, the angular position increases progressively to reach a plateau and then decreases again progressively in order to return to known angular positions. Thus, the angular positions reached at the time instants t0, t1, t2, t3 are identical to the angular positions reached respectively at the time instants t7, t6, t5, t4 as illustrated in [Fig.6].

[0065] With reference to [Fig.6], a second curve Cb shows the evolution of the attitude drift according to the prior art Daa and the evolution of the attitude drift according to the invention D. It is noted that in the prior art, the drift increases during over time and can become very high, which leads to significant inaccuracies. Conversely, thanks to the invention, it is noted that the drift is reduced each time the navigation device 3 returns to an angular position already encountered in the past (time instants t7, t6, t5, t4), that is to say, a reference attitude Ari determined in the database 33. As a result, the attitude drift D is corrected dynamically and can be contained over time. Thanks to the invention, it is possible to provide a precise attitude during the use of the optical system in order to carry out observations for several hours. Advantageously, the navigation device 3 retains a low mass, a reduced size and is low energy consumption so that it can be used during military operations.

Claims

Claims

1. Navigation device (3), configured to be mounted securely on an optical system (1) for aiming and observing a scene (SC), the navigation device (3) being configured to determine a navigation attitude (An), the navigation device (3) comprising: • at least one inertial module (31), configured to determine a current inertial attitude (Ac) continuously, • at least one vision module (32), configured to capture at least one current image (IMc) of the scene (SC) continuously, the inertial module (31) and the vision module (32) being physically secured in their movements, • at least one database (33) storing a plurality of reference attitudes (Ari), each reference attitude (Ari) being associated with a reference optical signature (Sri),• at least one computer (34) configured to: • Compare the current inertial attitude (Ac) with the reference attitudes (Ari) so as to determine the closest reference attitude (Arp) and deduce therefrom the associated reference optical signature (Srp), • Compare the current image (IMc) captured by the vision module (32) with the associated reference optical signature (Srp) so as to determine an angular offset (A), • Determine the navigation attitude (An) from the closest reference attitude (Arp) and the angular offset (A).,

2. Navigation device (3) according to claim 1, wherein the computer (34) is configured to determine the associated reference optical signature (Srp) only when the difference between the current inertial attitude (Ac) and the closest reference attitude (Arp) is less than a predetermined attitude threshold (Sa).

3. Navigation device (3) according to one of claims 1 to 2, in which the computer (34) is configured to determine a new reference attitude (Ari) associated with a new reference optical signature (Sri) when the difference between the current inertial attitude (Ac) and the closest reference attitude (Arp) is greater than a predetermined attitude threshold (Sa).

4. Navigation device (3) according to claim 3, in which the new reference attitude (Ari) corresponds to the current inertial attitude (Ac) and the new reference optical signature (Sri) is determined from the current image (IMc).

5. Navigation device (3) according to one of claims 1 to 4, in which the calculator (34) is configured to estimate, on the one hand, a first uncertainty for the current inertial attitude (Ac) and, on the other hand, a second uncertainty for the navigation attitude (An), the calculator (34) being configured to use the current inertial attitude (Ac) as the navigation attitude (An) if the first uncertainty is less than the second uncertainty.

6. Assembly of an observation system (1) and a navigation device (3) according to claims 1 to 5.

7. An assembly according to claim 6 in which the observation system (1) is in the form of optronic binoculars or a terrestrial sight.

8. Method for determining a navigation attitude (An) by a navigation device (3) according to one of claims 1 to 5, the navigation device (3) being mounted securely on an optical system (1) for aiming and observing a scene (SC), the method comprising steps consisting of: • Comparing the current inertial attitude (Ac) with the reference attitudes (Ari) so as to determine the closest reference attitude (Arp) and deducing therefrom the associated reference optical signature (Srp), • Comparing the current image (IMc) captured by the vision module (32) with the associated reference optical signature (Srp) so as to determine an angular offset (A), and

9. • Determine the navigation attitude (An) from the nearest reference attitude (Arp) and the angular offset (A). Determination method according to claim 8 comprising a step consisting of initializing the current attitude (Ac) by an astral sighting device.

Images